For me it was always very interesting to learn what minimum equipment is needed to make EME QSOs, especially on 23cm. I extended a W2IMU feed made of 6mm mesh by adding a large cone, achieving a horn antenna with 80cm mouth diameter. Estimated gain is 19dBi, maybe slightly less.

A spare 80W SSPA was used for the transmit side. Together with the horn I got 49dBm+19dB=68dBm EIRP.

First tests were made in combination with my 7.3m offset dish. I was transmitting with the dish, reducing transmit power step by step down to 10W. At this level I still could occasionally see traces of the echos on Spectran waterfall.

Next was receiving the beacon ON0EME with the horn antenna. The signal was found immediately, clearly visible on Spectran and WSJT, audible most of the time when it transmitted carrier. CW was not readable, only sometimes a letter or fragments. The level in WSJT was between -20 and -22dB, on occasion -19dB. Probably I loose 1dB or 2dB due to some extra noise pickup because of the broader lobe.

Measuring echo strength with different antenna combinations

Weak but traces detectable: echos at my 3m dish when transmitting with 80W at the 80cm horn

Next: transmitting again with 80W into the horn, receiving with 7.3m offset dish

Testing echos was good to learn what is possible with such a small station, and it was also nice to confirm previously made calculations. But making QSOs with that setup was another challenge.

During the 2016 ARRL EME contest I worked within a couple of hours on Oct 22nd several stations in WSJT using the 80cm horn antenna and 80W, all random:

0646 HB9Q (-9 -21), 0658 UA4HTS (-12 -22),

0709UA3PTW(-13 -19), 0746RA3AUB(-20 -24),

0811 DF3RU (-20 -?), 0831 OK1KIR (-17 -23)

I did not use deep search and deleted call3.txt. HB9Q has a 10m dish, all the other stations I worked have dish size around 6m. As we can see from the receive reports between -12 and -20 for them, it should be possible to decode stations using a 3m dish and good power.

As a result from my measurements, together with experiences from the past, I tried to find a simple formula to calculate what equipment is necessary on 23cm to detect echos, make QSOs in WSJT (assuming decode at -25, no deep search and call3.txt), CW and SSB (depending on personal skills).

Calculation is based on antenna gain of station A(dBi), antenna gain of station B(dBi) and power in dBm. For example, a 3m dish has about 30dB gain, a 6m dish 36dB gain, 250W is 54dBm. The result in this case is 30dB+36dB+54dBm=120dBm.

To demonstrate
what is possible with EME, I made moonecho tests
on 70cm between my 10m dish with
31dBi, and a dual-dipole antenna
with 10dBi, widely used as a
feed for a dish. The audio samples below
demonstrate the signal quality when transmitting
with the big dish and receiving with the small
antenna ( and vice versa).

On March 19th 2000, I worked
on 23cm 10 stations random within 3 hours,
transmitting with this small antenna. Highlight
was the QSO with ZS6AXT, who is using a 5 meter
dish. I could even hear my moonechos receiving
with the big dish, when I transmitted with the 1
meter horn and only 50 Watts.

Here you can see the ´big´ horn made
of mesh wire. It is 2.3m long. The picture on the right side
shows this ´EME´-antenna in its operating
position: feedpoint indoors, and the cone looking
outside through the shack window.